Due to the limited reserves of fossil fuels and worries about emission of greenhouse gases there is an increasing focus on using renewable energy sources.
Production of fermentation products from lignocellulose-containing material is known in the art and includes pre-treating, hydrolyzing, and fermenting the lignocellulose-containing material.
The fermentation step is carded out using a fermenting organism capable of converting fermentable sugars into the desired fermentation product. After the fermenting organism is inoculated into the fermentation medium it passes through a number of phases. The initial phase is referred to as the “lag phase” and is a period of adaptation where no significant amount of fermentation product is produced. During the next two phases referred to as the “exponential phase” with increased growth and the “stationary phase”, which is the phase after maximum growth, significant amounts of fermentation product are produced. Fermentation cycles typically can go on for up to 96 hours or more, making each cycle time consuming and expensive.
The processes for producing fermentation products from lignocellulose-containing materials or cellulosic “biomass” is also limited by the tolerance of the fermenting organism to the many toxins found in the crude hydrolyzates used in the fermentation process. Removal of the toxins from the hydrolyzate is difficult, time consuming, and expensive. To avoid the costly toxin removal step, the percentage of solids in the hydrolyzates is conventionally kept below 10% total solids (w/w), thus minimizing the effect of the toxins on the fermenting organism. Unfortunately, limitation of total solids concentration means less available fermentation substrate and lower fermentation product yield per batch.
Thus, it is highly desirable to utilize crude hydrolyzates with high total solids concentration and decrease fermentation time necessary for producing a desired fermentation product from lignocellulose-containing material.